2009年1月15日 星期四

Application of genetics II

Procedure of artificial selection:
  1. select individual with best character
  2. breed them using sexual reproduction
  3. best offspring selected and breed again together
  4. this is repeated over generations until offspring have all the desired characteristics
Hybrid Vigour
They are individuals that are heterozygous for a number of different gene
They often show greater fitness, e.g. better growth, productive, disease resistant
The reason for it may not clear as gene may affect more than one trait and heterozygotes may benefit from the effects of a number of different interactions

Polyploidy
cell or organism conains three or more times the haploid number
sterile hybrid: odd number of set of chromosome
fertile hybrid: even number

Inbreeding and Outbreeding:
both are selectively controlled reproduction
Inbreeding:
between closely related individual, e.g. between offsprings, parent and child
+To maintain desirable characteristics
-cause reduced fertility and lowered disease resistance as variation reduced
therefore it is not favoured by animal breeders

Outbreeding:
between member of genetically distinct populations, e.g. different strain or different specises
+introduce new and superior phenotype by gene interaction--heterosis, hybrid vigour

Genetic modification
Method
  1. increase activity of gene
  2. decrease ...
  3. transfer gene between same or different species
Purpose(3 is enough)
  • increasing the yield
  • improving nutrient content of foods
  • introducing resistance to disease and pests
  • making crop plants tolerant to herbicides
  • developing tolerance to environmental condition-hazards
  • making vaccines
  • producing medicines

Cloning
Cloning is the process of producing populations of genetically-identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments (molecular cloning), cells (cell cloning), or organisms.

Cloning by nuclear transfer:
1. Donor cell taken
  • it is culture in low nutrient medium
  • nutrient deprived cell stop dividing
  • active gene switched off and become dormant
2. Unfertilized egg has nucleus removed
3. Cells are fused
  • 1st electric pulse
  • time delay allow unknown factors in the cytoplasm to activate chromatid
4. Cell division is triggered
  • 2nd electric pulse
5. Embryo surgically implanted into the uterus of the surrogated mother


resource from wiki

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